1. Field of the Invention
The present invention relates to an oil supply system of an automatic transmission, and more particularly, to an oil supply system of an automatic transmission that supply oil from an oil reservoir to a high-pressure part for operating a clutch and to a low-pressure part for cooling and lubricating, using an oil pump.
2. Description of Related Art
As the oil price increases and the regulation for exhaust gas (CO2) is enhanced over the world in recent years, it is very important to improve fuel efficiency and consider eco-friendly factors in developing vehicles and the advanced car manufacturers have devoted all their strength to come up with technologies for saving fuel in order to achieve those objects.
Improving power transmission efficiency the transmission is necessary to improve fuel efficiency in automatic transmission vehicles, but the oil pump in the automatic transmission is a part reducing the power transmission efficiency, such that the power transmission efficiency of the transmission can be considerably increased, if unnecessary power consumption of the oil pump can be reduced.
The output flow rate of the oil pump is composed of the flow rate of the high-pressure part for operating the clutch, the flow rate of the low-pressure part for cooling and lubricating, and the recirculation flow rate returning the flow rate left after generating desired oil pressure from a regulating valve to the inlet of the oil pump, however, the oil supply systems discharges the entire oil on the basis of the high-pressure part used to control the clutch in the related art, such that the oil pump consumes a large amount of power and accordingly the power transmission efficiency of transmissions is reduced.
That is, according to an oil supply system of the related art, as shown in FIG. 1, an inlet 1a of an oil pump 1 is connected with an oil reservoir 3 through an oil supply channel 2, an outlet 1b of oil pump 1 is connected to a high-pressure part 5 for operating a clutch through a high-pressure part channel 4, high-pressure channel 4 is connected with a high-pressure regulating valve 8 and a reducing valve 9 through a first valve channel 6 and a second valve channel 7, respectively, reducing valve 9 is connected to a low-pressure part 11 for cooling and lubricating through a low-pressure part channel 10, and high-pressure regulating valve 8 and reducing valve 9 are connected with oil supply channel 2 through a first return channel 12 and a second return channel 13, respectively.
In this configuration, oil 14 in oil reservoir 3 is supplied to inlet 1a of oil pump 1 through oil filter 15 and oil pump 1 is operated by power from an engine 16.
Therefore, as oil pump 1 is operated by the power from engine 16, oil 14 in oil reservoir 3 flows into inlet 1a and the oil discharged from outlet 1b to high-pressure part channel 4 is controlled at high pressure by high-pressure regulating valve 8 and supplied to high-pressure part 5.
Some of the oil in high-pressure part channel 4 is supplied to reducing valve 9 through second valve channel 7, reducing valve 9 reduces high pressure of the oil to low pressure, and the oil at the low pressure reduced by reducing valve 9 is supplied to low-pressure part 11.
Further, the oil left from the oil increased in pressure by high-pressure regulating valve 8 recirculates to inlet 1a of oil pump 1 through first return channel 12 and oil supply channel 2 and the oil left from the oil decreased in pressure by reducing valve 9 recirculates to inlet 1a of oil pump 1 through second return channel 13 and oil supply channel 2.
In general, since low-pressure part 11 is used to cooling and lubricating the transmission, it needs a lot of flow rate, while since high-pressure part 5 is used to control the clutch, it needs a smaller amount of flow rate than low-pressure part 11.
Therefore, according to the oil supply system having the configuration of the related art, oil pump 1 discharges the entire flow rate on the basis of high-pressure part 5, such that oil pump 1 requires a large amount power. For example, assuming that high-pressure part 5 requires pressure of 20 kgf/cm2 and flow rate of 5 lpm, low-pressure part 11 requires pressure of 8 kgf/cm2 and flow rate 10 lpm, and the recirculation flow rate is 15 lpm, the consuming power of oil pump 1 of the system according to the related art is defined by “consuming power=high-pressure part pressure×entire discharged amount”, and substituting values in the equation, “20 kgf/cm2×30 lpm=980 W”, that is, the consuming power of oil pump 1 is 980 W.
The consuming power 980 W of oil pump 1 is relatively large and the large consuming power of oil pump 1, as described above, considerably reduces the power transmission efficiency of the transmission, such that the fuel efficiency of the vehicle reduces. Further, excessive load is applied to oil pump 1, such that durability of oil pump 1 is reduced and large noise is caused. Pressure vibration is excessively generated by cavitation when oil pump 1 operates at high speed.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.